High-throughput screening typically requires parallel processing of batches of samples, typically in multiple well plates (MWPs) of 24, 48, 96, and 384, or more, wells per plate. MWPs are standard sizes that can be used with existing high-throughput machinery, such as with robotic-controlled pipetters. Each pipetting station of a robotic controlled pipetter employs pipetting heads having an array of pipette tips that address multiple wells simultaneously. Although used effectively for the screening of liquid samples, the current multiple well plates are generally ineffective for screening plant and other tissues, and the secretory products associated with these tissues, that require, or prefer, more complex environments such as solid support structures.
For example, attempts have been made to grow plants in MWPs by suspending the plants in a liquid media within each well. However, the plant tissue is deprived of oxygen when sitting in the liquid, effectively “drowning” the plant tissue in an anaerobic environment. Other attempts have been made using media that are generally more solid and provide a substrate on which the plant tissue may be supported above the fluid, such as a gel or filter paper disk. Although these types of supports avoid drowning the plants, they are difficult to exchange and replenish when the nutrients or media have been depleted. Paper bridges doused in liquid media have also been used as tissue supports and the liquid media is somewhat more easily replenished. However, empirical evidence has shown that paper bridges are difficult to manage in an automated system and are generally ineffective at promoting plant tissue growth. Without being wed to any particular theory, this may be because the liquid media does not easily penetrate the paper bridge (i.e., the paper bridge is only mildly hydrophilic) and the tissue supported thereon lacks a continuous supply of media.
A common approach to supplying fresh media to plant tissue is to move the plant tissue to a container holding fresh media. Movement of the plant tissue is a relatively slow and labor intensive process, as multiple plates must be replenished and otherwise prepared for each batch of plant tissue. In addition there is a threat of loss or contamination of the tissue samples when they are removed from the wells.
Another approach to aspirating and removing spent media and tissue byproducts is to use an assay plate having a plurality of wells, with each well having a hole or port at the base of the well. A filter is positioned at the bottom of each well to support the tissue. Spent media can be vacuum harvested from each well through the port using a vacuum manifold assembly., One example of a vacuum manifold assembly is the MultiScreen Vacuum Manifold system manufactured by MILLIPORE of Bedford, Mass. The assay plate rests on a manifold that supplies a vacuum which draws the media through the filter disks, out of the cell wells and through the ports, where it is captured in the manifold below. Although the filter disks in the assay plate allow media to be drawn out of the plate, it is difficult for the filter disks to retain enough media to support tissue maintenance and growth for any length of time. Because the ports at the bottom of the wells are open to the ambient air, the ports may allow media to leak or evaporate and may also provide a path for microbial contamination of the wells. In addition, the wells of the assay plate cannot be individually sampled because the vacuum manifold harvests the media from all of the wells at once.
The tissue of animals, and other types of organisms may also require, or prefer, solid support structures that inhibit the use of multiple well plates and high-throughput screening techniques. For instance, the growth of cartilage cells may be promoted by the use of a collagen fibril matrix that simulates an in vivo environment. Similar to the plant tissue discussed above, the cartilage cells need a supply of fresh media that is replenished at various intervals to survive and/or proliferate. In addition, some of the cartilage cells proliferate within the collagen fibril matrix and cannot be moved independent of the matrix. Moving the cells to a new plate with a fresh supply of media requires movement of the entire collagen matrix which is a relatively slow and inefficient process that exposes the tissue to contamination.
It would be advantageous to have a multiple well plate that allows the use of high throughput screening methods for non-liquid samples. In addition, it would be advantageous to have a multiple well plate that allows the use of high throughput screening methods for tissues that require, or prefer, solid support structures. It would be further advantageous to have a multiple well plate that promotes the growth of tissue, such as plant tissue, without posing the risk of drowning the tissue in liquid media or allowing the tissue to dehydrate or become contaminated. It would also be advantageous to have a multiple well plate that allows media to be easily replenished, without undue disturbance of the tissue contained in the wells. Additionally, it would be advantageous to have the capability of sampling less than the total number of wells in the plate without disturbing the unsampled wells.